tigefa4u projects Trac

The main idea of the original refactoring has been kept: don't render the events directly when generating them, but defer this last step when the event is actually processed within the template.

But instead of requiring a intermediate `TimelineEvent` object, we now rely on a `render_timeline_event` method of the `ITimelineEventProvider` to do the job. The event itself is still a tuple, but of different arity than the one of 0.10, so that we can easily make the difference and keep backward compatibility. The new tuple enable the components to add an arbitrary amount of "private" data to the tuple, for the rendering needs